Historically, bedding fabrics used in the industrial environment, e.g. in hospitals, hotels and the like have been made from natural fibers such as cotton. Bedding materials made from cotton fabric, however, lack the strength and durability required when the products are to be subjected to the relatively more harsh institutional or industrial launderings, because fabrics made of cotton tend to lose fiber density due to fiber breakage in response to abrasion. Therefore, bedding articles made from cotton fabric tend to become thin after a relatively low number of uses and launderings resulting in a useful life that is undesirably short.
To enhance fabric strength, cotton fibers are sometimes blended with synthetic fibers such as polyester to form bedding fabrics. While providing improved fabric durability over 100% cotton fabrics, even these blended fabrics cannot normally withstand repeated launderings at the high pH levels and temperatures of institutional or industrial launderings. Therefore, the life span of the blended fabrics also tends to be undesirably low. For example, conventional cotton/polyester blended sheets usually survive only about 70-120 institutional washes at their relatively elevated pH levels and temperature.
Fabrics and bedding articles from 100% synthetic fibers such as polyester also have various drawbacks. Fabrics formed from continuous filament polyester tend to be very durable; however, they have an undesirable hand and can be unsatisfactory to consumers. Fabrics made from staple polyester, while having a more desirable hand, suffer from a propensity to acquire a large number of pills on their surfaces when they are used. Fabric pilling results from abrasion of the fabric surface which causes damage to protruding staple fibers. Although some fibers, such as cotton, are sufficiently weak that abrasion causes breakage and shedding of the fibers and fiber pieces, higher tenacity fibers such as polyester are not normally broken by abrasion. Instead the fiber ends stretch and wrap together into small balls or pills. Thus following substantial use the fabric can have a high number of pills on its surface resulting in an undesirable surface texture, particularly for bedding applications such as sheets.
Substantial efforts by numerous concerns including fiber manufacturers, fabric manufacturers, chemical concerns and others, have been directed over many years in various efforts to reduce the pilling of polyester fabrics. One such method involves abrading the fabric surface in order to weaken the fibers so that broken fiber pieces can be more readily released from the fabric surface. For example, U.S. Pat. No. 2,706,845 to Swan discloses a method of imparting pill resistance to a fabric containing synthetic staple fibers by brushing the fabric to disfigure the fibers and thereafter locking the disfigured fiber ends in the fabric surface by shrinking. Another example, U.S. Pat. No. 3,894,318 to Ito et al, discloses a method of enhancing pilling resistance of fabrics containing synthetic staple fibers by contacting the fabric surface with an abrasive surface to form defects in the fibers distributed along the fabric surface. Still other efforts have been directed to weakening the fiber structure by various chemical treatments; however, these efforts, when successful, also reduce fabric durability.
One hundred percent (100%) polyester fabrics also typically suffer from very low moisture absorbency, particularly in woven products such as sheets, and are considered by some consumers to have a "clammy" feel. This is generally believed to be due to the hydrophobic nature of polyester.
Many finishes which adhere well to cellulosic fibers such as cotton do so because they are able to bond with the --OH groups of cellulosic fibers. Because polyester has essentially no free surface groups available for bonding, the finishes which adhere well to other materials such as cotton fibers do not tend to adhere well to polyester. Typically, finishes applied to fabrics formed from polyester fibers tend to wash off of the fabrics as a result of repeated launderings.
Thus despite substantial effort and research, fully satisfactory polyester fabrics suitable for bedding and the like which are resistant to the formation of pills and capable of withstanding numerous launderings at institutional or industrial temperature and pH levels are still not available. Likewise, non-pilling polyester which is both durable and absorbent is still the subject of significant research, but with little success.